CVE-2026-80920: io_uring: defer eventfd signaling when queued from a wakeup handler

CVE-2026-80920: io_uring: defer eventfd signaling when queued from a wakeup handler

[Greg Kroah-Hartman]

From: Greg Kroah-Hartman <gregkh@kernel.org>

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

io_uring: defer eventfd signaling when queued from a wakeup handler

io_req_local_work_add() signals the CQ ring eventfd inline when it is the
one to push the first entry onto ->work_list. For DEFER_TASKRUN rings that
add is frequently done from a waitqueue wakeup handler, where an
arbitrary waitqueue lock is held.

eventfd_signal_mask() only refuses to recurse when current->in_eventfd
is set, but that bit is set by eventfd_signal_mask() itself. If the wake
chain starts somewhere else, signal goes out inline and can feed back
into epoll.

Add IOU_F_TWQ_IN_WAKE, set it on the task_work add done from the three
waitqueue callbacks, and use it to force io_eventfd_signal() down the
existing call_rcu_hurry() deferral instead of signaling inline.

The Linux kernel CVE team has assigned CVE-2026-80920 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 6.1 with commit 21a091b970cdbcf3e8ff829234b51be6f9192766 and fixed in 6.18.49 with commit e22f4494cc9487d326e5e3067f33dea7c1e442b2
	Issue introduced in 6.1 with commit 21a091b970cdbcf3e8ff829234b51be6f9192766 and fixed in 7.1.11 with commit b6bb334b0e9348887e3e55e1f494b0c3b8fbf59f
	Issue introduced in 6.1 with commit 21a091b970cdbcf3e8ff829234b51be6f9192766 and fixed in 7.2.1 with commit 40b6ccf68731809ceb85c6e9f0f8f2ed61c7aa5a
	Issue introduced in 6.1 with commit 21a091b970cdbcf3e8ff829234b51be6f9192766 and fixed in 7.3-rc1 with commit cd305ee3633a45fcf5f3a5d83f99f3cb77d87b6e

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-80920
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	include/linux/io_uring_types.h
	io_uring/eventfd.c
	io_uring/eventfd.h
	io_uring/futex.c
	io_uring/io_uring.c
	io_uring/poll.c
	io_uring/tw.c
	io_uring/waitid.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/e22f4494cc9487d326e5e3067f33dea7c1e442b2
	https://git.kernel.org/stable/c/b6bb334b0e9348887e3e55e1f494b0c3b8fbf59f
	https://git.kernel.org/stable/c/40b6ccf68731809ceb85c6e9f0f8f2ed61c7aa5a
	https://git.kernel.org/stable/c/cd305ee3633a45fcf5f3a5d83f99f3cb77d87b6e